Just noticed the discussion with interest as I am currently investigating this exact issue (ARP4). There are truths lurking in many of these posts however: -
1. Pad material selection for an OEM is always a balance of many criteria - often conflicting. Friction is only one (but the most important) of these criteria.
2. As expressed above, hard/soft refers to the range of temperatures over which effective/consistent operation is assured.
3. Friction materials have dynamic/kinetic friction properties and also static friction properties.
4. The relationship between these 2 properties is not linear - meaning you can have (relatively) high static but low dynamic and vice versa.
5. Assuming the car is stationary then the static friction properties are of course the key. And it is quite possible to find a pad material with higher static friction but which doesn't significantly affect braking balance dynamically.
6. Don't forget that front/rear brake balance changes in all cars over temperature (even if material is the same front and rear the spot temperatures will not be). In most road cars this balance change is not critical - especially when you have ABS (whats that Morgan ask?) - but its the reason race cars have adjustable front/rear brake balance.
7. So for an ARP4 the holy grail is rear pad material with higher static friction with broadly similar dynamic friction levels at typical operating temperatures.
All of the above is of a lower order of significance than cable routing/sticking, lever installation issues etc. So needless to say you need to be sure these are all addressed first.
Alternatively save time, ignore the problem, leave it in gear and/or take a chock with you :-).
